So I tried to find a good how-to for integrating steam big picture into my mythbuntu based mythtv installation. It turns out the change is fairly trivial. All you have to do is add a button entry to /usr/share/mythtv/themes/defaultmenu/mainmenu.xml like the below diff.

--- mainmenu.xml.orig	2016-07-24 23:56:30.918935677 -0500
+++ mainmenu.xml	2016-07-25 01:03:48.061586983 -0500
@@ -16,6 +16,13 @@
     </button>
 
     <button>
+        <type>GAME</type>
+        <text>Steam Games</text>
+        <description>Launch Steam Big Picture Mode</description>
+        <action>EXEC steam -bigpicture</action>
+    </button>
+
+    <button>
	 <type>MENU_INFO_CENTER</type>
	 <text>Information Center</text>
	 <description>Information and Communications</description>

However when exiting steam, you have to select to exit steam instead of the other options. This way mythtv regains focus again. There is probably a way to accomplish this, but I haven’t yet spent the time to figure it out.

Enjoy!